Stereoregulated polymerization in the free propagating species. I. Theory

Abstract

The theoretical aspects of a new method of regulating the steric structure in addition polymers are treated. The basic principle utilized is the directing force at the free end of the propagating species, as contrasted to the influence of a bound initiator. Only small differences in the free energies of activation of the isotactic and syndiotactic propagations are required for relatively significant changes in polymer structure, particularly at low polymerization temperatures. Both the relative amounts of the two configurations in the polymer and the distribution of individual sequence lengths bear a simple relationship to the two propagation constants. In the analogous rotational isomerism, the free energy difference between the gauche and trans conformations is known to be influenced by both steric and electrostatic factors. For molecules of the type ACH2CH2A, the difference in heat content is increased by an increase in the size or the polarity of the substituents and, for polar substituents, by a decrease in the dielectric constant of the medium. Steric and electrostatic factors at the free end of the growing polymer chain can, in theory, influence the structure in polymers. This conclusion is based on an estimate of steric and electrostatic energy components of the most probable conformational arrangements for the isotactic and syndiotactic configurations in representative polyvinyl chloride with theoretical structure. The refinement introduced by bond angle deformation can also be approximated for the two polymer configurations. With respect to each of the three energy components the syndiotactic configuration is the preferred structure, in agreement with known experimental results that polyvinyl chloride prepared under free radical conditions does contain syndiotactic sequences sufficiently long for x‐ray detection. The combined, alternate use of the directing force at the free end of the propagating species and that of a bound initiator to form syndiotactic–isotactic block copolymers is suggested.

Stereocontrol in the free-radical polymerization of methacrylates with fluoroalcohols

“…Even equimolar or lower amounts of (CF 3 ) 3 COH to MMA enhanced the syndiospecificity of the polymerization (Table IV, 6). Although the enhancement of the polymer yield and molecular weight of the products became less obvious with a decrease in the amount of (CF 3 ) 3 COH, a syndiotactic polymer was obtained in a 17% yield with 0.1 equiv of (CF 3 ) 3 COH (Table IV, 1), whereas the polymerization in toluene at the same temperature gave a polymer in only a 2% yield (Table II, 5).…”

Poly(vinyl alcohol) with High Diad-Syndiotacticity and High Melting Point

“…2 During the course of study, radical polymerization of VP in various solvents was examined and non polar solvents were favorable for syndiotactic propagation. 3 Lower temperatures give rise to higher syndiotacticity in radical polymerization of vinyl esters, 4 and even a slight difference in tacticity of PV A substantially affects physical properties.…”

Temperature dependence of stereospecificity in the radical polymerization of di-n-butyl itaconate in bulk

“…14 Figure 2 shows the temperature dependence of tacticity in the radical polymerization of DBI in bulk. 15 Two linear dependencies with different slopes were observed from Ϫ78 to 30°C and 50 to 120°C, although only one linear dependence was observed for the polymerization of common monomer such as methacrylates and vinyl esters. The difference in activation enthalpy (⌬H ) and the difference in activation entropy (⌬S ) between isotactic and syndiotactic propagation can be determined by the plots according to the following equation:…”